A shortcut function for install.packages() and library()

I enjoy trying difference kind of R packages. Since I have more than 1 computers (1 at home, 1 at office and a laptop)
it is troublesome to check whether I have installed some new packages for each computer. Therefore i wrote a function to load and install packages at once. If the package does not exist, then the it will be downloaded from CRAN and be loaded it.